Towards Highly Efficient Electric Vehicle Powertrains: Architecture, Control, and Thermal Management

Abstract

Battery electric vehicles are central to the transition toward sustainable road transport, yet their widespread adoption remains constrained by limited driving range and the cost, mass, and environmental burden associated with larger battery packs. Improving powertrain energy efficiency offers an alternative route to extend driving range without increasing battery capacity. This thesis investigates system-level methods for enhancing BEV powertrain efficiency through coordinated developments in powertrain architecture, control, and thermal management.This thesis first examines powertrain architectures that introduce additional operational degrees of freedom. A dual-motor powertrain with disconnect functionality is investigated, where front and rear electric drive units can be selectively decoupled to eliminate no-load losses. An energy management strategy is developed to optimize operating mode selection and torque distribution while accounting for transient synchronization losses. Simulation results show that the proposed configuration reduces WLTC energy consumption by 8.21% compared with a conventional dual-motor powertrain. In addition, a configuration-aware motor design optimization framework is proposed to tailor the front and rear motors to the added flexibility, providing a further reduction in energy consumption.This thesis also investigates control-oriented approaches for improving powertrain efficiency. For a single-motor powertrain with disconnect functionality, an eco-driving strategy is developed to exploit free-coasting through predictive optimization of traction torque and clutch state. Results show that energy consumption can be reduced by up to 11.6% on representative real-world routes. Furthermore, a torque modulation strategy is proposed to improve efficiency at low load by replacing continuous low torque operation with pulsating torque commands of equal average value. The modulation strategy is optimized at the whole-powertrain level and shown to reduce WLTC energy consumption by 1.05\% for a single-motor powertrain and 2.21% for a dual-motor powertrain, while maintaining acceptable driver comfort.The thesis further studies adjustable DC-link voltage as an additional efficiency measure. By introducing a bidirectional DC-DC converter between the battery and inverter, the DC-link voltage can be adapted to the operating condition to minimize the powertrain losses. Results show that this approach can reduce WLTC energy consumption by up to 3.25%, with larger benefits at low battery state of charge and when SiC-based power electronics are used. The thesis further studies adjustable DC-link voltage as an additional efficiency measure. By introducing a bidirectional DC-DC converter between the battery and inverter, the DC-link voltage can be adapted to the operating condition to minimize the powertrain losses. Results show that this approach can reduce WLTC energy consumption by up to 3.25%, with larger benefits at low battery state of charge and when SiC-based power electronics are used. Further analysis with a high-voltage 900 V battery system shows that the adjustable DC-link voltage is not only beneficial for conventional 300–400 V architectures but also applicable to emerging high-voltage platforms.Finally, this thesis develops an energy-efficient thermal management strategy. By coordinating coolant flow, oil flow, radiator fan operation, and active grille shutter position, the controller minimizes the combined energy consumption of the powertrain and its auxiliaries while respecting component temperature limits. Compared with a conventional rule-based strategy, the proposed method reduces energy consumption in both urban and highway driving.In summary, this thesis presents a comprehensive study on efficiency-oriented design and control of battery electric vehicle powertrains. The results show that significant energy savings can be achieved by systematically introducing and exploiting additional degrees of freedom in powertrain architecture, operation, and thermal management.